Ornamental and decorative light displays utilizing incandescent lamps with plugs and sockets interconnected by flexible wires has long been a commonly accepted technique for carrying power to the lamps and allowing flexibility in forming the display. This same arrangement is also used to supply power using Light Emitting Diodes (LEDs). The nature of the LED allows both static and dynamic operation, single and multicolor. That is, the device can be operated by both constant battery voltage or an oscillating voltage. This oscillating voltage can be a two level signal, of varying amplitude, or pulse width modulated.
Bedmars/Electro-Harmonix in U.S. Pat. No. 4,264,845 uses a plurality of generating means for producing a plurality of sets of binary signals of different periods. The configuration of the LED arrays described in this patent are also in common use such as LED bar graph displays in both matrix and linear configuration. This patent also makes no allowance for low power or minimization of numbers power conductors.
Holiday and other ornamental lamp systems have typically utilized the socket and bulb approach where an incandescent lamp is threadedly engaged with a complementary threaded socket. These systems use an extraordinary amount of power for the light generated, particularly given the purpose, have a relatively short life span of about one thousand to ten thousand hours of use, require substantial surge current when placed in operation and are generally not reliable. In addition they are rather difficult to store. Since the incandescent lamps are typically made of thin glass bulbs, they are exceptionally fragile and often will break when stored or sometimes when in use. In addition to the deficiencies discussed above, there are certain safety factors which detract from use of incandescent lamps such as the heat that they generate and the potential for shorts causing shocks and fire hazards if the shorts and the heat are generated in or around particularly dry or otherwise flammable material.
LEDs have been used in certain instances in an ornamental manner but have found rather limited use due to their design and configuration. LEDs have been mounted on a tape to permit certain configurations of numbers which can be adhered to a relatively flat surface. As ornamental lights used in the holiday season are particularly price sensitive, the manner of fabrication, the configuration of the elements and their ability to withstand wear are factors normally weighed by consumers and producers in arriving at an economically marketable item.
The invention described herein overcomes many of the problems discussed above. An advantage of the lighting system of the invention revolves around its simplicity of manufacture, a configuration which is highly durable and lends itself to permanence in addition to a long life and low power requirements. Applicant's invention utilizes LED lamps which operate from a low voltage direct current power such as batteries or typical alternating source with a transformer rectifier for converting the household alternating current to direct current for use with the lights. Both systems utilize the same light strings each having thirty to fifty-two individual lamps. The lifetime of the individual lamp is typically one hundred thousand hours. If used continuously the lights can be expected to burn for over ten years. The power unit is fused and provided with 115/230 volts selection compatible with domestic and international markets. The light strings are designed to further overcome the necessity of plugging each string into the power source. Rather the system provides the user with the ability to plug one set of lights into the power unit and the second set of lights into the first, the third and second etc.
Much of the problem with incandescent lights is the deterioration of the sockets from one season to the next. The sockets are inexpensively made and corrode causing poor or intermittent connections. The wires in these lights are wrapped around the contacts and there is no positive joint as would be found if the connections were soldered. Connections between the lamp terminals and the metal contact is a pressure only.
The invention described herein uses an insulation piercing connection with the lamp and socket being a single molded assembly. The wire is conductive stranded similar to stereo speaker wire where a number of conductors are housed in the same insulation package or can be separately insulated. LED lamps are highly shock resistant and provide significant advantages over incandescent bulbs which can shatter when shocked or vibrated in the on condition. These LED lamps do not radiate heat; and the non-photon (or heat) energy is dissipated through the lamp leads. Incandescent lamps on the other hand radiate considerable heat through the lens. In addition, no surge current in a LED system is experienced contrary to the incandescent lamp situation when cold. Because of their configuration, shock resistance and other features, the LED lamp system can be mounted permanently without having to replace individual lamps. Incandescents are generally mounted in sockets which can be as expensive as the lamp itself. Not only does socket deterioration add to the unreliability of operation, but also incandescent lamps often must be replaced over the lifetime of the system.
A further embodiment of the invention allows for the use of light emitting diodes constructed of two or more individual diodes. These devices are fabricated in two configurations and are generally intended to be used as multiple state indicators. For example, a Bicolor Red/Green diode can indicate "Stop" or "Go" depending on which color is selected. However, if each color is alternately selected at a fast enough rate, the colors can blend to produce yellow. Further, if the proportion of red to green is varied, orange and amber as well can be produced. If it were technically possible to produce a true chromatic blue-green LED, the red and blue-green could be modulated to produce a white light.
Perhaps most importantly, particularly where a large number of strings are used, the LED system described herein operates at less than 13% of the current and less than 0.5% to 0.7% of the power as an incandescent tree light. Due to the fusing of the transfer system the low power or current draw and isolation from the household power source the LED system is significantly more safe than the incandescent and other system available for ornamental tree lamps. Since the LED system described herein is practically shock resistant it is easier to store than the incandescent light system.
The present invention provides an improved decorative lighting means using LEDs, CMOS integrated circuits and high current MOS (metal oxide semiconductor) transistors. The invention provides for an extremely large configuration of LEDs to be driven at low average power and at the same time allow the user to select individual lights to be constantly illuminated or flash in response to an oscillating voltage source or allow multicolor patterns to be generated using bicolor LEDs.
The LEDs are connected by flexible current carrying wires attached to individual plugs and sockets that accommodate the LED and a series current limit resistor. Three such conductors are provided. One wire provides connection to the positive side of a constant voltage source the second to a "low-side" switch to ground of the same constant voltage source. The third wire allows connection to a secondary oscillator that derives power from a first or primary oscillator.
In the non-flashing mode of operation, the LED lamp is mechanically connected from the positive voltage wire to the "low-side" switch. The LEDs are electrically in parallel across these two wires. The length of the wires is limited only by the ohmic resistance of the wire and the size of the voltage source. For convenience, the number of lamps can be limited and connectors provided for plugging more of the same identical wiring configurations together maintaining a three wire parallel electrical connection. The immediate implementation of the invention allows for four such combinations to be driven from individual "low-side" switches connected to the primary power source and oscillator. The switching occurs at a frequency such that the human eye cannot detect the on/off condition of the diodes, 1250 Hz for this implementation. Each parallel configuration of LEDs is in the on-state for 200 microseconds and off for 600 microseconds. No two configurations are on at the same time. The connection to ground through the low-side switch is alternately applied to one of the four configurations, each configuration being turned on for 200 microseconds once each 800 microseconds.
The main oscillator allows this basic frequency to be varied to the upper limit of the LED response and to a lower limit which is detectable to the human eye.
The secondary CMOS oscillator derives power from the primary oscillator via the positive voltage rail and the intermittent switching of the low-side switch to ground. This switching action causes a capacitor storage element to charge, through an isolation diode, toward the voltage of the positive supply rail. The diode prevents the capacitor from discharging through other parts of the system and therefore can only discharge into the secondary timing circuit. The second oscillator frequency is set for an on/off cycle of five seconds. This period can also be varied. The output of the oscillator drives a "high-side" power MOS transistor switch that applies the second timing pulse to the third wire. The lights are mechanically rotated in their socket so as to break the connection with the first, positive voltage rail, maintain contact with the low-side ground switch and connect with the third secondary oscillator high-side switch. The present implementation allows the high-side switch to be connected to the positive voltage rail for three seconds and disconnects the LEDS from this source for two seconds. In this way, individual lamps connected to the secondary oscillator can be illuminated constantly by connection to the positive voltage rail and the low-side switch or can be made to flash by physically rotating them to permit connection to the output of the high-side switch and the low-side switch. These combinations can be extended until the switching frequency of the main oscillator reaches a rate that can be detected by the human eye, approximately 100 Hz. If the on-time of the individual configurations of LEDs is maintained at 200 microseconds, 50 (fifty) such configurations could be driven. The present implementation has 38 LEDs in parallel per light string with two light strings per configuration connected via a plug/socket. This two string configuration is driven by a MOS power low-side switch. This means each switch is driving 76 LEDs at a peak current per LED of 25 milliamps or a total of 1.9 amperes peak. The voltage source is 6.5 volts, sufficient for driving at least 2 (two) configurations. This represents 6.5.times.1.9=12.35 watts peak. Since each configuration is on for only 200 microseconds out of 800 microseconds, this represents a duty cycle of 25% and the average power is 12.35.times.0.25 or 3.08 watts. This method of illumination, especially when applied to ornamental and seasonal decoration, is extremely safe compared to conventional methods.